1. Field of the Invention
The present invention relates to a tire pressure control system for a motor vehicle.
2. Background Art
A tire pressure control system monitors the pressure of the tires installed on the wheels of a vehicle. The tire pressure control system includes tire pressure sensors and a controller located in the vehicle. Each tire pressure sensor is respectively installed within one of the tires. As such, each tire pressure sensor is associated with a wheel (i.e., a wheel position). Each tire pressure sensor generates a tire pressure signal indicative of the pressure of the tire in which the tire pressure sensor is installed. The tire pressure sensors wirelessly transmit the tire pressure signals to the controller. The controller has to know which tire pressure signals correspond to which wheels. That is, the controller has to know which tire pressure sensors correspond to which wheel positions. This requirement is a problem as the tires may be rotated at any time such that the tires are installed on different ones of the wheels.
EP 1 052 119 A1 (corresponds to U.S. Pat. No. 6,435,020) describes a tire pressure control system operable for determining the association between the tire pressure sensors and the wheel positions. Each tire pressure sensor transmits, at certain time intervals, an individual identifier and a high-frequency (“HF”) signal to the controller. The HF signals have an individual trace which is dependent upon the rotational angle of the wheel and on the time because of the geometry of the wheel box and as a consequence of the wheel rotation. In the controller, a time point is fixed from two sequential HF signals at which the wheel assumes the same angular position in each case with this wheel being the wheel position from which the HF signals were transmitted. The corresponding wheel has made an integer number of revolutions between the two time points. In the controller, with the aid of rotational speed sensor signals indicative of the rotational speed of the wheels, the wheel position is determined in which the wheel has made an integer number of revolutions between the two time points. The corresponding wheel position is associated to the individual identifier transmitted from the tire pressure sensor.
A disadvantage of this tire pressure control system is that the tire pressure sensors transmit the HF signals to the controller thereby subjecting their internal power supplies to relatively heavy stress. Furthermore, this initialization process is regularly repeated such as each time the vehicle is started. A problem is that the internal power supplies are usually intended to only last for the typical service life of a tire.